Abstract:

A system and method for integrated thermal monitoring in Power over
Ethernet (PoE) applications. Headroom in a particular cable installation
is identified using ambient temperature measurement alone or in
combination with determined cable characteristics. In calculating an
amount of headroom for a particular cable installation, the current
capable of being carried over the cable would not be limited by
worst-case cable assumptions.

Claims:

1. A power over Ethernet method, comprising:measuring a characteristic of
an Ethernet cable by a physical layer device, said Ethernet cable
coupling a power sourcing equipment to a powered device;measuring an
ambient temperature using a temperature sensor associated with one of
said power sourcing equipment and said powered device; andcontrolling an
amount of power transmitted on said Ethernet cable based on said measured
characteristic and said measured ambient temperature, said controlling
including an analysis of said measured ambient temperature relative to a
threshold temperature rating.

2. The method of claim 1, wherein said measuring a characteristic
comprises measuring one of a cable length, resistance, insertion loss,
and cross talk.

3. The method of claim 1, wherein said measuring an ambient temperature
comprises measuring using a temperature sensor associated with said power
sourcing equipment device.

4. The method of claim 1, wherein said measuring an ambient temperature
comprises measuring using a temperature sensor associated with said
powered device.

6. The method of claim 1, wherein said controlling comprises changing a
current threshold.

7. The method of claim 1, wherein said controlling comprises changing a
power consumption at said powered device.

8. The method of claim 1, wherein said controlling comprises analyzing a
difference between said measured ambient temperature and a cable rating.

9. A power over Ethernet method, comprising:measuring an ambient
temperature using a temperature sensor associated with one of a power
sourcing equipment and a powered device, said power sourcing equipment
providing power to said powered device via an Ethernet cable; andreducing
a current threshold used by said power sourcing equipment on said
Ethernet cable based on said measured ambient temperature, said reducing
being based on an analysis of said measured ambient temperature to a
threshold temperature rating.

10. The method of claim 9, wherein said measuring comprises measuring
using a temperature sensor associated with said power sourcing equipment.

11. The method of claim 9, wherein said measuring comprises measuring
using a temperature sensor associated with said powered device.

[0003]The present invention relates generally to power over Ethernet (PoE)
systems and methods and, more particularly, to a system and method for
integrated temperature measurement in PoE applications.

[0006]In the PoE process, a valid device detection is first performed.
This detection process identifies whether or not it is connected to a
valid device to ensure that power is not applied to non-PoE capable
devices. After a valid PD is discovered, the PSE can optionally perform a
power classification. In a conventional 802.3af allocation, each PD would
initially be assigned a 15.4 W power classification after a Layer 1
discovery process. An optional classification process could then
reclassify the PD to a lower power level. For example, a Layer 2
classification engine can be used to reclassify the PD. In general, a
Layer 2 classification process can be included in PoE systems such as
802.3af, 802.3at or proprietary schemes. The completion of the power
classification process enables the PSE to manage the power that is
delivered to the various PDs connected to the PSE system.

[0007]In general, PoE is a relatively new application that is being
applied to an existing cabling infrastructure. Significantly, this
cabling infrastructure was not originally designed for the distribution
of power. Accordingly, the provision of power over the cabling
infrastructure can be impacted by the presence of heat, which reduces the
capacity of the cable to transmit power and data.

[0008]Heat can be present due to a variety of sources. For example, heat
can be present in the ambient environment or can be generated through the
transmission of current in the cable itself or in surrounding cables. PoE
systems must account for this heat during operation. These considerations
will play an even greater role in the administration of high-power PoE
systems such as that proposed by the IEEE 802.3at specification. What is
needed therefore is a mechanism that enables the PoE system to account
for the existence of heat in an active manner during system operation.

SUMMARY

[0009]A system and/or method for integrated temperature measurement in PoE
applications, substantially as shown in and/or described in connection
with at least one of the figures, as set forth more completely in the
claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]In order to describe the manner in which the above-recited and other
advantages and features of the invention can be obtained, a more
particular description of the invention briefly described above will be
rendered by reference to specific embodiments thereof which are
illustrated in the appended drawings. Understanding that these drawings
depict only typical embodiments of the invention and are not therefore to
be considered limiting of its scope, the invention will be described and
explained with additional specificity and detail through the use of the
accompanying drawings in which:

[0011]FIG. 1 illustrates an embodiment of a Power over Ethernet (PoE)
system.

[0012]FIG. 2 illustrates an embodiment of a PoE environment at a power
sourcing equipment.

[0013]FIG. 3 illustrates a flowchart of a process of integrating ambient
temperature measurements in a PoE process.

[0014]FIGS. 4 and 5 illustrate examples of current-temperature for a PoE
cable installation.

DETAILED DESCRIPTION

[0015]Various embodiments of the invention are discussed in detail below.
While specific implementations are discussed, it should be understood
that this is done for illustration purposes only. A person skilled in the
relevant art will recognize that other components and configurations may
be used without parting from the spirit and scope of the invention.

[0016]FIG. 1 illustrates an embodiment of a power over Ethernet (PoE)
system. As illustrated, the PoE system includes power sourcing equipment
(PSE) 120 that transmits power to powered device (PD) 140. Power
delivered by the PSE to the PD is provided through the application of a
voltage across the center taps of transformers that are coupled to a
transmit (TX) pair and a receive (RX) pair of wires carried within an
Ethernet cable. In general, the TX/RX pair can be found in, but not
limited to structured cabling. The two TX and RX pairs enable data
communication between Ethernet PHYs 110 and 130 in accordance with
10BASE-T, 100BASE-TX, 1000BASE-T, 10GBASE-T and/or any other layer 2 PHY
technology.

[0017]As is further illustrated in FIG. 1, PD 140 includes PoE module 142.
PoE module 142 includes the electronics that would enable PD 140 to
communicate with PSE 120 in accordance with a PoE standard such as IEEE
802.3af, 802.3at, legacy PoE transmission, or any other type of PoE
transmission. PD 140 also includes pulse width modulation (PWM) DC:DC
controller 144 that controls power FET 146, which in turn provides
constant power to load 150.

[0018]In the example of the IEEE 802.3af standard, PSE 120 can deliver up
to 15.4 W of power to a plurality of PDs (only one PD is shown in FIG. 1
for simplicity). In the IEEE 802.at specification, on the other hand, a
PSE can deliver up to 30 W of power to a PD over 2-pairs or 60 W of power
to a PD over 4-pairs. Other proprietary solutions can potentially deliver
even higher levels of power to a PD. In general, high power PoE+solutions
are often limited by the limitations of the cabling.

[0019]In the IEEE 802.3af standard, each wire conductor has a specified
current limit of 175 mA, resulting in a total specified current limit of
350 mA. The 802.3at specification identifies higher wire conductor
current limits to accommodate higher power applications. Regardless of
the current limits that have been defined for a particular PoE
application, one of the key considerations is heat.

[0020]Heat can greatly impact system performance. As the temperature goes
up, cable attenuation also increases. For certain cable types, for
example, cable attenuation can increase at a rate of 0.4% for every
degree Celsius above 20° C. This can continue up to a typical
cable temperature rating of 60° C. Heat can therefore have an
impact on data transmission. As heat can also change the DC resistance of
the cable, it also has an impact on the transmission of power over the
cable. More generally, heat has a direct effect on safety and the
long-term life expectancy of the cable itself.

[0021]In a PoE application, the net effect of the passage of current
through the wire conductor is a temperature increase of the conductor
itself. The heat generated by this temperature increase is then
dissipated into the environment. This dissipated heat is in addition to
the heat currently present as reflected by the ambient temperature.
Further exacerbating the situation is the diverse environments in which
the cable is placed. For example, increased heating can be experienced in
areas where airflow is restricted, such as in a cable conduit, wiring
closet, or the like. As typical installations include cables bundled
together or in close proximity, temperature effects are typically
magnified in areas where cable deployments are concentrated. For example,
it is not uncommon to see massive bundles of cables (e.g., 90-150)
leaving a data center or wiring closet.

[0022]One of the concerns of higher power PoE+ systems is the impact of
overly conservative temperature restrictions that are derived from
worst-case operating conditions. These overly conservative temperature
restrictions can significantly reduce the legitimate operating margins of
those PoE+ systems.

[0023]It is therefore a feature of the present invention that a measured
ambient temperature can be integrated into a PoE application on a per
port/channel basis to facilitate greater granularity in the PoE power
allocation/management process. In general, one of the goals of a per
port/channel ambient temperature integration is to ensure that an
imposition of a current limitation or power consumption restriction on a
port/channel is only performed when it is needed.

[0024]In conventional systems, there is typically no knowledge in the
physical subsystem of the ambient temperature. Accordingly, control in
the power allocation/management process would typically assume a
worst-case cable operating temperature. This leads to overly broad
restrictions.

[0025]FIG. 2 illustrates an embodiment of a PoE environment 200 at a PSE
location in which the principles of the present invention can be
implemented. As illustrated, environment 200 includes PHYs 216-1 to 216-N
that are each connected to Ethernet switch 214. While a PHY can include
one or more Ethernet transceivers, the wiring for only a single
transceiver is illustrated as being connected to PHY 216-N. As would be
appreciated, a PHY can be discrete or integrated as part of Ethernet
switch 214. Each PHY is also connected to CPU 212, although only a single
connection from CPU 212 to PHY 216-N is shown for simplicity. In one
embodiment, CPU 212 is incorporated along with Ethernet switch 214 and
PHYs 216-1 to 216-N on a single chip 210. In another embodiment, Ethernet
switch 214 and PHYs 216-1 to 216-N are incorporated on a single chip
separate from CPU 212, wherein communication with CPU 212 is enabled via
a serial interface. Also illustrated in PoE environment 200 is a PSE 220
that provides power through the center taps of the transformers shown. As
illustrated, PSE 220 is also coupled to CPU 212 via opto-isolator 230
that facilitates an isolation boundary.

[0026]To illustrate the operation of PoE environment 200 in implementing
the principles of the present invention, reference is now made to the
flowchart of FIG. 3. As illustrated, the process begins at step 302,
where one or more characteristics of a cable are examined using a
physical layer device. In various examples, the examined cable
characteristics can include the cable length, resistance, insertion loss,
cross talk, etc. In one embodiment, these cable characteristics would be
examined periodically during the provision of power on the particular PoE
channel.

[0027]In one embodiment, a transceiver in PHY 230-N performs measurements
of an Ethernet cable coupled to PHY 230-N. In one embodiment,
measurements that enable a determination of cable length, resistance,
insertion loss, cross talk, etc. can be taken during an echo canceller
convergence process performed by an echo canceller module under control
of CPU 210. Cable characteristic measurements taken by the transceiver
are then transmitted to CPU 210. In an alternative embodiment, the cable
characteristic measurements could also be taken by the Ethernet
transceiver at the PD either alone or in combination with the transceiver
in PHY 230-N.

[0028]At step 304, an ambient temperature is measured. In general, the
ambient temperature can be measured using one or more temperature sensors
that are associated with a PD and/or PSE subsystem. In various
embodiments, the temperature sensor can be designed to take a temperature
reading on or near a chip, inside a chassis, outside a chassis, inside an
equipment room, or any other location that would enable measurement of an
ambient temperature relevant to a cable. If the temperature sensor is on
a chip or in a chassis, then an ambient temperature can be inferred.

[0029]At step 306, the ambient temperature, alone or in combination with
the cable characteristics, can be used to determine a baseline reference
point. In other words, the initial data that is obtained at steps 302 and
304 would enable the system to establish a reference point by which the
system operation can be monitored and controlled in the future.

[0030]At step 308, a change in the ambient temperature is identified. This
change in ambient temperature can be identified through the periodic
monitoring of ambient temperature readings that are taken by one or more
temperature sensors. As would be appreciated, the ambient temperature
readings at the PSE or PD side of the system can be used, For example, an
ambient temperature reading at the PD side can be used in an analysis at
the PSE side, or vice versa.

[0031]At step 310, the identified change in the ambient temperature, alone
or in combination with other cable characteristic data, can be used to
determine a potential impact on the PoE system. In one embodiment, the
determination is performed by CPU 210. In another embodiment, the
determination is performed by PSE 220, which receives the measurements
from CPU 212. Regardless of where the determination is performed, its
availability to PSE 220 would enable PSE 220 to determine its impact on
the PoE system configuration and/or operation.

[0032]In the process of step 310, the change in ambient temperature would
be identified relative to the baseline reference point. This identified
change can be used to recalibrate various aspects of PoE system
operation. For example, an increase in ambient temperature Y from the
baseline temperature reference point can lead to an inference that the DC
cable resistance would increase by Y from the baseline DC cable
resistance reference point. This identified increase in the DC cable
resistance reference point can lead the system to determine that the
transmission of power over the cable may need to be reduced or otherwise
controlled in some fashion. As would be appreciated, the particular
methodology by which an identified ambient temperature change would
impact the PoE system operation would be implementation dependent.

[0033]In general, the PoE system impact analysis can be performed at the
PSE and/or PD. For example, the analysis can be performed at the PSE
using data that is generated at the PSE and/or PD. In another example,
the analysis can be performed at the PD using data that is generated at
the PSE and/or PD. If the data is generated remotely from the point of
analysis, then the data communication can occur via a Layer 1 scheme,
such as voltage and/or current modulation, Layer 2 (packets), Layer 3
(packets), or any such combination. Packets may be a standard protocol
such as Ethernet, LLDP, OAM, or a proprietary system over these
protocols.

[0034]In various embodiments, the potential impact can consider a change
in operation of a single PoE channel, or a group of PoE channels. For
example, if the determined change in temperature indicates that a given
cable has reached a temperature that is above an allowable threshold
(e.g., 60° C., 75° C., etc.), then the system can choose to
reduce or cut the power being applied to that PoE channel. In another
example, the system can choose to reduce or cut the power being applied
to a group of PoE channels, if it is known that the heat in a given cable
could impact the operation of other cables, for example, where the cables
are bundled together.

[0035]As noted, one of the features of the present invention is that a
measured ambient temperature can be integrated into a PoE application on
a per port/channel basis to facilitate greater granularity in the PoE
power allocation/management process. As illustrated in FIG. 4, the amount
of current that can be carried over a cable can be related to an ambient
temperature using a curve having a negative slope. In FIG. 4, the
current-temperature curve is illustrated as a linear relationship for
simplicity. This negative slope represents the impact of ambient
temperature on the current carrying capacity of a cable as it approaches
its cable rating (e.g., 60° C., etc.). With knowledge of such a
relationship, the PSE/PD can be designed to control the amount of power
that is transmitted/received over the cable based on the measured ambient
temperature. As the ambient temperature increases, for example, the
PSE/PD can be designed to reduce the amount of current that is
transmitted/received over the cable.

[0036]In one example, a derating curve based on the cable rating and the
ambient temperature can be used to determine the current over the cable.
FIG. 5 illustrates one example of a derating curve. In this example, the
greater the difference between the cable rating and the ambient
temperature, the greater the allowable current. In other words, the
positive-slope derating curve (shown as a linear relationship for
simplicity) enables greater levels of current over the cable if the
temperature of the cable reflected by the ambient temperature is farther
below the cable temperature rating. As would be appreciated, the
particular shape of the curves illustrated in FIGS. 4 and 5 can be based
on theoretical cable characteristics or actual cable characteristics.

[0037]In general, the use of the ambient temperature measurement enables
the system to determine an amount of headroom remaining in the cabling
for PoE current transmission. Without the ambient temperature
measurement, the system would need to assume a conservative amount of
headroom that is derived from a worst-case operating condition. Excess
headroom in a particular cable installation would therefore be left
unused.

[0038]In one embodiment, the ambient temperature measurement can also be
combined with determined cable characteristics to produce a more accurate
analysis of the headroom available for a particular cable installation.
Here, knowledge of the ambient temperature can be used in combination
with characteristics such as cable length, DC resistance, insertion loss,
cross talk, etc. to determine the exact amount of current that can be
sent through that cable. For example, if it is known that the cable
connecting the PSE and PD is Cat 5 cable with a length of 60 m, then the
system could determine that the DC resistance or insertion loss would be
X at temp Y. The headroom present can then be deduced using the available
temperature and cable characteristic information.

[0039]As would be appreciated, the particular mechanism by which the
headroom would be determined would be implementation dependent. What is
key, however, is that the information gained through temperature sensors
positioned at one or more points would enable the system to more
accurately calculate a cable temperature using various calibration
schemes. Once a cable temperature is calculated, the system can then
determine how much current to use for that particular cable installation.
Significantly, this determination is based on the characteristics of that
particular installation, not a worst-case scenario.

[0040]It should be noted that the principles of the present invention can
be applied to any form of network cabling, whether standard Ethernet
cabling (e.g., Category 3, 5, 6, etc.) or to non-standard cabling such as
Type-II cabling.

[0041]These and other aspects of the present invention will become
apparent to those skilled in the art by a review of the preceding
detailed description. Although a number of salient features of the
present invention have been described above, the invention is capable of
other embodiments and of being practiced and carried out in various ways
that would be apparent to one of ordinary skill in the art after reading
the disclosed invention, therefore the above description should not be
considered to be exclusive of these other embodiments. Also, it is to be
understood that the phraseology and terminology employed herein are for
the purposes of description and should not be regarded as limiting.